Hydraulically set liner hanger

ABSTRACT

A liner hanger, in either a non-rotating or rotating format, has a large hanging capacity due to a one or more axially spaced sets of circumferentially spaced slips housed in openings in a slip housing, the slip housing being moveable axially relative to a mandrel for actuating the slips over cams supported by the mandrel. One or more sets of sets of slips are spaced axially along the slip housing. An annular space is formed between the mandrel and slip housing for maximizing fluid bypass through the annular space. Bypass is further improved by profiling the slip housing. In the rotating version, a separate sleeve is positioned between the mandrel and the slip housing for supporting the cams and the mandrel is supported on the cam sleeve through an upper bearing which permits the mandrel to rotate on the cam sleeve when the slips are set.

FIELD OF THE INVENTION

[0001] The invention relates to liner hanger apparatus used for carrying and anchoring a casing liner in a wellbore casing.

BACKGROUND OF THE INVENTION

[0002] Liner hangers are well known in wellbore drilling and completion operations. Following drilling of at least a segment of a wellbore, a metallic casing is positioned into the open hole and cemented into place. Drilling is continued below the cemented casing to extend the depth of the wellbore. At least a second length of smaller diameter casing is lowered into the extended wellbore on a tubular workstring equipped with a liner hanger and is positioned near a bottom end of the existing cemented casing. Typically, liner hangers are equipped with mechanically or hydraulically actuated slips which, when actuated downhole, act to grip the walls of the existing casing and support the substantial weight of the depending liner until such time as the new liner can be cemented into place. This procedure may be repeated more than once, until the wellbore has reached an effective depth, the diameter of each subsequent length of liner being smaller than the previous.

[0003] Hanger capacity, the amount of weight the hanger can support, is of great concern. Ideally, in order to keep the effective diameter of the wellbore within acceptable limits, it is desirable to hang as long a length of liner as can be supported by the liner hanger.

[0004] Attempts have been made to improve hanger capacity by increasing the number of slips and their arrangement in the tool. U.S. Pat. No. 4,926,936 to Braddick teaches a liner hanger having a plurality of circumferentially and vertically spaced slips. Cones for actuation of a plurality of slips are attached to a tubular body using rings and are positioned relative to slips which are attached by arms to a sleeve which overlies the body and is axially moveable thereon, the entirety of the arms and slips being vulnerable to mechanical contact as the hanger is run into the wellbore. Axial movement of the sleeve, either mechanically or hydraulically, engages the slips with the cones causing the slips to engage the casing. The number of vertical sets of slips which equates to the liner hanger's support capability is limited by the space between the lower circumferentially spaced slips which is required to accommodate the arms extending vertically from the sleeve. Further, fluid passage in the annular space between the casing and the liner hanger is impeded as the number of slip arms increases. Typically, there is little clearance between the outer surfaces of the liner hanger wall and the casing so as to permit the largest possible bore through the center of the liner hanger.

[0005] U.S. Pat. No. 4,603,743 to Lindsey Jr. teaches a hydraulically or mechanically set liner hanger having tandem, longitudinally spaced slips extending on straps from a tubular cage member, which is axially moveable on a tool body. The slips are held in a retracted position by a running tool as the liner hanger is run into the wellbore. A pressure housing on the running tool is axially moveable on the running tool's mandrel and is actuated to shift, causing the cage on the liner hanger to shift, engaging cam faces on a slip expander housing and causing the slips to move outwards into engagement with the casing. The expander housing has rectangular openings which extend through the wall of the housing. A tieback sleeve is located below the liner hanger and above the liner. The position of the tieback sleeve, in combination with the rectangular openings in the housing, prevents its use for incorporating a liner top packer into Lindsey's liner hanger system.

[0006] Liner hangers are known wherein the liner can be rotated, not only during insertion into the wellbore, but also during cementing following setting of the liner hanger slips. Depending upon the circumstances, it may be advantageous to rotate the liner during cementing such as to ensure a uniform distribution of cement in the casing annulus as well as proper displacement of the drilling mud, without channeling of the cement through the mud. U.S. Pat. No. 5,181,570 to Allwin et al., U.S. Pat. No. 5,048,612 to Cochran and U.S. Pat. No. 4,848,462 to Allwin, teach rotatable liner hangers.

[0007] During cementing excess drilling fluid is displaced upwardly between the liner hanger and the cemented casing. Restriction in the fluid flow is undesirable.

[0008] There is a need for a liner hanger system having a large hanging capacity to permit hanging of long or heavy lengths of liner and maximum fluid bypass to eliminate any problems with fluid flow during cementing. Preferably, the slips should be protected from damage as a result of irregularities in the borehole. Ideally, the liner hanger should have a simplified manufacture. Ideally, liner hangers having these characteristics should be available in both non-rotating and rotating configurations for use in a wide variety of cementing operations.

SUMMARY OF THE INVENTION

[0009] Generally, a liner hanger comprises a slip housing axially moveable over a mandrel. The slip housing has a plurality of slip openings which contain slips. Relative axial movement of the slip housing over the mandrel cause actuation of the slips over cams supported on the mandrel. Fluid flow bypass is increased between the hanger and the casing by implementing additional bypass between the mandrel and the slip housing in an annular space formed therebetween. Bypass is unimpeded therein due to the circumferential arrangement of spaced slips. Sets of slips can be positioned axially along the length of the slip housing. The plurality of sets of slips results in an increased hanging capacity. The number of sets that can be applied is limited only by the length of the slip housing itself. Preferably, fluid bypass is further increased by profiling an inner surface of the housing.

[0010] In one broad aspect of the invention, a non-rotatable liner hanger comprises: a tubular mandrel having a slip housing axially moveable thereon and defining an annular space therebetween, the slip housing having an inlet and an outlet for permitting the flow of fluids through the annular space; one or more sets of slips housed in a plurality of openings in the slip housing and more preferably two or more sets of slips, each slip in each set of slips being spaced circumferentially for passage of fluids therebetween, each of the one or more sets of slips being spaced axially along the slip housing, preferably biased into the slip housing in a stowed position during running of the tool; cam surfaces extending radially outward from the mandrel and corresponding with each slip; and an actuator attached to the mandrel for axially moving the slip housing for engaging the slips with the cam surfaces and causing the slips to move from the stowed position to a radially extended position for engaging the existing casing.

[0011] The cam surfaces are supported by the mandrel and extend radially therefrom, preferably machined from an external surface of the mandrel to improve structural rigidity. The cam surfaces can alternatively extend from a cam sleeve positioned rotationally between the slip housing and the mandrel.

[0012] In a second broad aspect of the invention, a rotatable liner hanger comprises incorporation of the cams on a sleeve between the slip housing and the mandrel. Accordingly the rotatable liner hanger comprises: a tubular mandrel having a slip housing axially moveable thereon and defining an annular space therebetween, the slip housing having an inlet and an outlet for permitting the flow of fluids through the annular space; one or more sets of slips housed in a plurality of openings in the slip housing and more preferably two or more sets, each slip in a set of slips being spaced circumferentially for passage of fluids therebetween, each of the one or more sets of slips being spaced axially along the slip housing; a cam sleeve rotationally supported in the annular space, the cam sleeve having cam surfaces extending radially outward for urging the slips on the slip housing to a radially extended position while permitting the mandrel to rotate freely when the slips engage the casing; and hydraulic means attached to the mandrel for axially moving the slip housing for engaging the slips with the cam surfaces and causing the slips to move to a radially extended position for engaging the existing casing.

[0013] In both the rotating and non-rotating embodiments, the means acting between the slips and the slip housing to bias the slips into the slip housing during running in of the tool are springs attached to the slips and extending laterally therefrom between the slip housing and the mandrel.

[0014] Preferably, the hydraulic means or actuator for actuating the slip housing to move axially to set the slips is a piston in fluid communication with the bore of the mandrel, such that pressure in the bore to causes the piston to move uphole and actuate the slip housing.

[0015] Optionally, both rotating and non-rotating embodiments may have a collet system which acts to prevent premature axial movement of the slip housing while running in the tool. The collet system is positioned between the hydraulic section and the slip housing. A shear screw acts to retain a collet retainer between a collet housing and collet fingers to prevent the collet from releasing from a profile in the mandrel until such time as the mandrel's bore is pressurized sufficiently to actuate the piston in the hydraulic section. Both the retainer shear screw and a main shear screw between the collet housing and the mandrel must be sheared to permit actuation of the slips.

[0016] Further, in the rotating embodiment, so as to avoid imparting rotational energy to the hydraulic section, the piston is preferably formed in two sections, a lower section carrying seals which can rotate with the hydraulic section and an upper section which bears against the non-rotating collet retainer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a longitudinal partial sectional view of a liner hanger of the present invention;

[0018]FIG. 2 is a cross-sectional view according to FIG. 1, sectioned along lines A-A and showing the slips in a retracted position;

[0019]FIG. 3 is a cross-sectional view according to FIG. 1, sectioned along lines A-A and showing the slips in an extended position;

[0020]FIG. 4a is a front perspective view of a slip removed from the slip housing;

[0021]FIG. 4b is a rear perspective view of the slip according to FIG. 4a, illustrating the positioning of a laterally extending spring connected to the slip;

[0022]FIG. 5a is a rollout view of a slip housing having two sets of vertically positioned slips and illustrating, in dashed lines, a pattern of a flow of fluids between the plurality of slips;

[0023]FIG. 5b is a rollout view of a slip housing having two tiers of vertically positioned slips and option flow openings and illustrating, in dashed lines, a pattern of flow of fluids between the plurality of slips;

[0024]FIG. 6a is a longitudinal sectional view of a hydraulic portion of the liner hanger according to FIG. 1, the right side illustrating a non-actuated position and the left side illustrating an actuated position;

[0025]FIG. 6b is a sectional view of an optional collet system the right side illustrating a non-actuated position and the left side illustrating an actuated position;

[0026]FIGS. 7a-c are partial longitudinal sectional views of a second embodiment of the invention in which the casing can be rotated during cementing, illustrated in sections, FIG. 7a being an uphole section, FIG. 7b being an intermediate section and FIG. 7c being a downhole section, all of which are shown in a non-actuated position;

[0027]FIG. 8 is a partial longitudinal view illustrating embodiments of the liner hanger according to FIGS. 1 and 7a-c and optionally having either a single set of slips, two sets of slips or three sets of slips; and

[0028]FIG. 9 is a longitudinal, partially sectioned view of a liner hanger assembly including the liner hanger according to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] Having reference to FIGS. 1-3, a first non-rotating embodiment of a liner hanger 10 of the present invention is shown in a wellbore casing 11. The liner hanger 10 comprises an uphole slip portion S and a downhole hydraulic portion H for actuating the slip portion S. The liner hanger 10 has a tubular mandrel 12 having cam faces 13 supported by and extending radially outward therefrom. For additional structural integrity, the cam faces 13 are machined integral from the mandrel.

[0030] A slip housing 14 is mounted on the mandrel 12 and is axially moveable thereon. A plurality of openings 15 are formed in the slip housing 14 to accommodate a plurality of slips 16. The slips 16 are pivotally retained within the slip housing 14 and are normally retracted within the openings 15. A slip housing/mandrel annulus 18 is formed between the slip housing 14 and the mandrel 12. The slip housing/mandrel annulus 18 acts to provide additional fluid bypass for the flow of drilling fluids, displaced upwardly, during cementing.

[0031] Laterally extending biasing means 17, shown in greater detail in FIGS. 4a-4 b, are connected between the slips 16 and the slip housing 14, extending across and beyond each opening 15. The biasing means 17 act to normally retract the slips 16 into a radially stowed position in the openings 15 in the slip housing 14, during insertion of the liner hanger 10 into the casing 11. In operation, the slip housing 14 is caused to move axially on the mandrel 12 so as to engage the slips 16 with the cam faces 13 resulting in extension of the slips 16 into engagement with the casing 11 for gripping the casing 11 and supporting a liner (not shown) extending therefrom.

[0032] In a preferred embodiment, as shown in FIGS. 4a, 4 b and 5, the laterally extending biasing means 17 is a flat spring 19 and each slip 16 is attached to the corresponding spring 19 using a fastener 20, such as a screw. Additionally, as shown in FIG. 5a, mechanical, cantilevered supports, formed as tabs 21, extend from the slip housing 14 into opposing sides of each opening 15 at a downhole end 22 of each slip 16 to ensure the slips 16 remain biased to slip housing 14 and to assist in supporting the slips 16 when extended to grip the casing 11. The supports are formed as tabs 21 on either side of the opening 15, rather than as a solid bar across the opening 15, to ensure that the support will bend rather than break under stress should the casing 11 be oversized and the slips 16 over-extend to grip the casing 11.

[0033] Preferably, the slip housing 14 is assembled as two or more clam-shell portions assembled over the mandrel 12 and welded together, such as through section ring portion at the uphole and downhole ends of the slip housing.

[0034] Further, as shown in FIG. 5a, the slip housing 14 is slit, above and below each tab 21 at an interface 34 between the tab 21 and the slip housing 14, to decrease bending stress rather than risk breaking of the tab 21 under undue stress. The slit 35 is locally widened at a distal end 36 to avoid a stress concentration.

[0035] The slip housing 14 has a plurality of fluid inlet ports 30 formed at a downhole end 31 of the slip housing 14 and a substantially circumferential outlet 32 formed at an uphole end of the slip housing 14.

[0036] As shown in FIGS. 2, 3 and 5 a, the annulus 18 can be further increased in cross-sectional area to provide increased fluid bypass. The slip housing 14 is profiled on an inner surface 33 to provide the increased fluid flow bypass F by creating the enlarged annular space 18 between the mandrel 12 and the slip housing 14. The profiling can be a simple concavity resulting in a thinning of the wall of the slip housing 14.

[0037] The fluid flow bypass aids in passing well fluids during operations for cementing the newly hung liner into the wellbore. Cement is pumped through a bore in a liner hanger system, which simplistically includes a running tool suspended from a tubing string to surface and connected at a downhole end to the liner hanger, the depending liner and at a distal end to a float shoe. As cement exits the float shoe and rises to fill an annulus between the casing 11 and the open wellbore (not shown), drilling fluid is displaced upwards and must pass by the liner hanger 10. When the drilling fluid reaches the cemented casing 11, the fluid is forced between the liner hanger 10 and the casing 11. The displaced fluid enters the casing annulus 40 between the casing 11 and the liner hanger 10 and also enters the annulus 18 through the inlet port 30 between the slip housing 14 and the mandrel 12. Accordingly, displaced fluid can flow through a large cross-sectional area, including both the casing annulus 40 and the slip housing/mandrel annulus 18. The profiling of the inner surface 33 of the slip housing 14 further increases the annular 18 flow area.

[0038] As shown in greater detail in FIG. 5a, the slips 16 are positioned circumferentially and vertically about the slip housing 14. The number of slips 16 that can be positioned vertically, in tiers, is only limited by the length of the slip housing 14. The more slips 16 present, the more the load from the depending liner is distributed, thus increasing hanger capacity. Flow of drilling fluids F continues substantially unimpeded through the slip housing/mandrel annulus 18 regardless of the number of tiers of sets of slips 16.

[0039] Optionally, as shown in FIG. 5b, a plurality of additional openings 15 are formed in the slip housing 14 to further improve fluid access to the annulus 18 and improve fluid flow bypass.

[0040] Referring again to FIG. 1, the hydraulic section H of the liner hanger 10 is located on the mandrel 12 adjacent the downhole end 31 of the slip housing 14 and is adapted to actuate the slip housing 14.

[0041] As shown in greater detail in FIG. 6, a tubular piston housing 50 is formed around the mandrel 12 creating a cylindrical space 51 therebetween that is in fluid communication with a bore 52 of the mandrel 12 through a port 53. A piston 54 is positioned within and extends above the cylindrical space 51 and is axially moveable therein. During operation, an increase in pressure within the mandrel bore 52 which acts on a distal end 55 of the piston 54 moves the piston 54 to an uphole actuated position. A shear screw 56 between the slip housing 14 and the mandrel 12 acts to prevent actuation of the piston 54 until such time as the bore pressure acting upon the piston 54 creates a force sufficient to overcome the shear screw 56. The piston 54 acts on the downhole end 31 of the slip housing 14 to shift the slip housing 14 axially uphole, causing the slips 16 to extend and engage the casing 11.

[0042] In a preferred embodiment of the invention, the piston housing 50 is retained on the mandrel 12 using a split ring 57 and a ring retainer 58. The piston housing 50 is further secured to the ring retainer 58 using a set screw 59.

[0043] Having reference to FIGS. 6a-6 b and more preferably, the slip housing 14 is further temporarily restrained from axial movement during running into the wellbore by a collet system 60. The collet system 60 comprises a tubular collet housing 61, a collet 63 and a profile 66 in the mandrel 12. The tubular collet housing 61 is formed over the mandrel 12 immediately adjacent to and engaging the downhole end 31 of the slip housing 14, forming a downhole-facing annular space 62 therebetween. Shear screw 56 connects the collet housing 61 to the mandrel 12 thereby restraining the slip housing 14. The collet 63 is connected, preferably by threads 64, to the collect housing 61 in the annular space 62.

[0044] In a non-actuated position, a plurality of shaped distal ends 65 of the collet 63 reside in the profile 66 in the mandrel 12, locking the collet 63 and slip housing 14 to the mandrel 12. A tubular collet retainer 67 temporarily resides between the distal ends 65 and the collet housing 61 to retain the collet's distal ends 65 in the profile 66 and lock the collet housing 61 and slip housing 14.

[0045] The collet retainer 67 extends from an upper end 68 of the piston 54 to the collet 63. The retainer 67 is profiled forming an annulus 69 between the collet retainer 67 and the mandrel 12. An uphole end 70 of the retainer 67 protrudes between the collet housing 61 and the distal end 65 of the collet 63, for retaining the shaped end 65 of the collet in the profile 66. Shear screw 71 connects between the collet housing 61 and the collet retainer 67 to prevent the collet 63 from moving out of the profile 66 enabling axial movement of the piston 54 resulting in accidental setting of the slips 16.

[0046] In operation, uphole, axial movement of the piston 54 causes the piston 54 to bear upon the collet retainer 67, shearing the collet shear screw 71. The collet retainer 67 moves axially uphole into the annular space 63 between the collet housing 61 and the collet 63. An enlarged, shaped inner surface 72 of the collet retainer 67 permits the distal end 65 of the collet 63 to release from the profile 66 and move into the annular space 69. The uphole end of the retainer 69 acts upon the collet housing 61 causing shear screw 56 to shear and enabling the collet housing 61 to shift the slip housing 14 to the actuated position.

[0047] Having reference to FIGS. 7a-c, a second, rotating embodiment of the present invention is shown. The uphole slip portion S comprises a tubular mandrel 112, connectable at a top end 113 to a tubing string (not shown) and at a lower end 114 to a liner (not shown). A slip housing 115 is mounted on the mandrel 112 and as axially moveable thereon and forms an annular space 116 therebetween. The slip housing 115 supports slips 16 as detailed in the previous embodiment. A cam sleeve 117, having cam surfaces 118 extending radially outward, is positioned within the annular space 116. Openings or windows 119 are formed in the cam sleeve 117 below the cam surfaces 118 to permit the slips 16 to recess deeper in the radially stowed position. The mandrel 112 and the depending liner are supported on an upper bearing 120 positioned at a shoulder 131 on the mandrel 112 and an uphole end 132 of the cam sleeve. Preferably, the upper bearing 120 is a tapered roller thrust bearing. An uphole facing shoulder 121 on the mandrel 112 supports a lower end 122 of the cam sleeve 117.

[0048] The slip housing 115 and mandrel 112 are connected for co-axial movement by a shear screw 130 located in a groove 131 on the mandrel 112 permitting the slip housing 115 to rotate independent of the mandrel 112 prior to setting of the slips 16. The hydraulic section H is as described in the previous embodiment. Once the shear screw 130 has been sheared for actuation of the slips 16, the mandrel 112 and the connected, depending liner (not shown) are rotationally supported on the cam sleeve 117 through bearing 119. The mandrel 112 can be freely rotated within the cam sleeve 117, while the cam sleeve 117 and slip housing 115 are held stationary in the casing 11.

[0049] Preferably, to avoid imparting rotational or torsional energy to the hydraulic section H, the piston 54 is formed in two sections, a lower section 132 carrying seals 133 which rotates with the mandrel 12 and an upper section 134 which bears upon the non-rotating collet retainer 67.

[0050] As shown in FIG. 8, the liner hanger 10 is preferably available having one, two or three sets of slips 16 in either a rotating or a non-rotating embodiment. The hanging capacity is increased with the increasing number of sets of slips 16. The liner hanger having three sets of slips is better seen in FIGS. 7a-c.

[0051] In Use:

[0052] In a preferred arrangement, as shown in FIG. 9, a liner hanger assembly 100 typically comprises, listed from an uphole end 101, a tieback receptacle 102 or optionally a liner top packer 103, a liner hanger 104, a depending liner 105 containing a hydraulically actuated landing collar 106, and, at a downhole distal end 107, a liner float shoe 108 forming a contiguous bore 109. The assembly 100 is attached to a running tool fluidly connected to a tubing string (not shown) for insertion into a previously cemented wellbore casing 11 (FIG. 1). During insertion, the slips 16 are held in the retracted or stowed and protected position as a result of the laterally extending springs 19. The piston 54, in the hydraulic section H, is in the non-actuated downhole position. The collet system 60 prevents premature actuation of the slips 16, which could otherwise result from mechanical interference in wellbore or as a result of minor pressure increases.

[0053] The liner hanger system 100 is lowered through the cemented casing 11 to a position near a lower end of the casing 11. A ball 110 is dropped through the contiguous bore 109 and is caught in the landing collar 106. Once caught, the ball 110 blocks the bore 109, permitting pressure to be applied above the ball 110 to shear the shear screws 71, 56 and actuate the hydraulic portion H of the liner hanger to move the slip housing 14 axially uphole to the actuated position causing the slips 16 to set and grip the casing 11.

[0054] To begin cementing, the bore 109 is pressured in excess of the slip actuation pressure to blow the ball 110 in landing collar 106 and re-establish fluid communication in the bore 109 with the float shoe 108. A pre-determined volume of cement is pumped through the bore 109 and out float shoe 108. As cement fills the annulus between casing and the borehole (not shown), drilling fluid is displaced up the annulus and into the casing annulus 40 and through the mandrel annulus 18 (FIGS. 2-3) at a joint between the old cemented casing 11 and new liner 105. The displaced fluid flows into the inlet ports 30 in the slip housing 14, between the slips 16 in the enlarged annulus 18 and exits through the outlet port 32 at the top of the slip housing 14.

[0055] In the case of the second embodiment described above for the rotating liner hanger, the mandrel 112 and depending liner can be freely rotated during placement of the cement.

[0056] To conclude the cementing operation, a drill pipe wiper (not shown) is dropped from surface into the bore 109 to follow the cement. The drill pipe wiper mates with a liner wiper at a bottom end of a running tool (not shown). The mated wipers are sheared under pressure to drop from the bottom of the running tool to latch into a landing collar 106 which results in a pressure spike indicating latching has occurred. Cementing is then stopped, after which the running tool is removed from the bore 109 and the top packer 103 is set. 

The embodiments of the invention in which and exclusive property or priviledge is claimed are defined as follows:
 1. A liner hanger for use in hanging a liner inside an existing casing in a wellbore, the liner hanger comprising: a tubular mandrel having a slip housing mounted thereon and defining an annular space therebetween, the slip housing being axially moveable upon the mandrel and having an inlet and an outlet for permitting the flow of fluids through the annular space; one or more sets of circumferentially spaced slips, each slip being housed in a slip opening in the slip housing, each of the one or more sets of slips being spaced axially along the slip housing, cam surfaces supported by and extending radially outward from the mandrel and corresponding with each slip; a spring for biasing each slip to a radially stowed position towards the mandrel; and an actuator attached to the mandrel for axially moving the slip housing and engaging the slips with the cam surfaces for causing the slips to move from the radially stowed position to a radially extended position for engaging the existing casing.
 2. The liner hanger as described in claim 1 wherein the slip housing is profiled so as to enlarge the annular space and thereby increase fluid flow bypass.
 3. The liner hanger as described in claim 1 wherein the spring is connecting between the slip housing and each slip.
 4. The liner hanger as described in claim 1 wherein the spring is a flat spring secured to each slip and extending either side of the slip opening for connecting between the slip housing and each slip.
 5. The liner hanger as described in claim 1 wherein the cam faces are integral with the mandrel.
 6. The liner hanger as described in claim 1 wherein the actuator is a hydraulic portion comprising: a tubular piston housing formed on the mandrel and defining an cylindrical space therebetween; and a piston positioned within the cylindrical space and axially moveable therein, the piston being in fluid communication with a bore of the mandrel for actuating the piston from a non-actuated, downhole position to an uphole actuated position as a result of pressure increases in the bore of the mandrel.
 7. The liner hanger as described in claim 1 further comprising a shear screw connected between the mandrel and the slip housing so as to prevent axial movement of the slip housing during insertion of the liner hanger into the wellbore.
 8. The liner hanger as described in claim 1 further comprising a collet system between the mandrel and the slip housing for temporarily retaining the slip housing in a downhole non-actuated position during insertion of the liner hanger into the wellbore.
 9. The liner hanger as described in claim 8 wherein the collet system comprises: a collet connected to the slip housing and normally engaged in a corresponding profile on the mandrel; a collet housing adapted to the slip housing and forming an annular space between the collet and the collet housing; a collet retainer positioned in the annular space in a downhole position for retaining the collet in the profile in the mandrel and axially moveable therein to an uphole position for releasing the collet from the profile in the mandrel; and a shear screw between the collet retainer and the collet housing for temporarily restraining the collet retainer in the downhole position.
 10. The liner hanger as described in claim 9 wherein the collet retainer further comprises a profiled inner surface for alignment with the collet when the collet retainer is moved axially uphole and accepting the collet when released radially from the profile in the mandrel
 11. The liner hanger as described in claim 1 further comprising mechanical supports formed on either side of the opening in the slip housing at a downhole end of the slips for further supporting the slips in the extended position.
 12. The liner hanger as described in claim 11 wherein the supports are tabs having slits formed in the housing above and below each tab, at an interface between the tab and the slip housing to ensure bending of the tab under stress
 13. The liner hanger as described in claim 1 wherein the slip housing further comprises a plurality of additional openings therethrough to improve fluid bypass.
 14. The liner hanger as described in claim 1 further comprising: a cam sleeve positioned between the mandrel and the slip housing and defining the annular space between the cam sleeve and slip housing, the cam surfaces extending radially outward from the cam sleeve; and an upper bearing for supporting the mandrel on the cam sleeve while permitting the mandrel to rotate relative to the cam sleeve and slip housing when the slips engage the casing.
 15. The liner hanger as described in claim 14 wherein the slip housing is profiled so as to enlarge the annular space and thereby increase fluid flow bypass.
 16. The liner hanger as described in claim 14 wherein the spring is a flat spring secured to each slip and extending either side of the opening for connecting between the slip housing and the slip.
 17. The liner hanger as described in claim 14 wherein the actuator is a hydraulic portion comprising: a tubular piston housing formed on the mandrel and defining an cylindrical space therebetween; a piston positioned within the cylindrical space and axially moveable therein, the piston being in fluid communication with a bore of the mandrel for actuating the piston from a non-actuated, downhole position to an uphole actuated position as a result of pressure increases in the bore of the mandrel; and a shear screw connected between the mandrel and the slip housing so as to prevent axial movement of the slip housing during insertion of the liner hanger into the wellbore.
 18. A liner hanger for use in hanging a liner inside an existing casing in a wellbore, the liner hanger comprising: a tubular mandrel having a slip housing mounted thereon and defining an annular space therebetween, the slip housing being axially moveable upon the mandrel and having an inlet and an outlet for permitting the flow of fluids through the annular space; two or more sets of circumferentially spaced slips, each slip being housed in a slip opening in the slip housing, each of the two or more sets of slips being spaced axially along the slip housing, cam surfaces extending radially outward from the mandrel and corresponding with each slip; a spring for biasing each slip to a radially stowed position towards the mandrel; and an actuator attached to the mandrel for axially moving the slip housing and engaging the slips with the cam surfaces for causing the slips to move from the radially stowed position to a radially extended position for engaging the existing casing.
 19. The liner hanger as described in claim 18 wherein the slip housing is profiled so as to enlarge the annular space and thereby increase fluid flow bypass.
 20. The liner hanger as described in claim 18 wherein the spring is a flat spring secured to each slip and extending either side of the opening for connecting between the slip housing and the slip.
 21. The liner hanger as described in claim 18 wherein the actuator is a hydraulic portion comprising: a tubular piston housing formed on the mandrel and defining an cylindrical space therebetween; a piston positioned within the cylindrical space and axially moveable therein, the piston being in fluid communication with a bore of the mandrel for actuating the piston from a non-actuated, downhole position to an uphole actuated position as a result of pressure increases in the bore of the mandrel; and a shear screw connected between the mandrel and the slip housing so as to prevent axial movement of the slip housing during insertion of the liner hanger into the wellbore.
 22. The liner hanger as described in claim 18 further comprising a collet system for temporarily retaining the slip housing in a downhole non-actuated position during insertion of the liner hanger into the wellbore, wherein the collet system comprises: a collet connected to the slip housing and normally engaged in a corresponding profile on the mandrel; a collet housing adapted to the slip housing and forming an annular space between the collet and the collet housing; a collet retainer positioned in the annular space in a downhole position for retaining the collet in the profile in the mandrel and axially moveable therein to an uphole position for releasing the collet from the profile in the mandrel; and a shear screw between the collet retainer and the collet housing for temporarily restraining the collet retainer in the downhole position.
 23. The liner hanger as described in claim 18 further comprising: a cam sleeve positioned between the mandrel and the slip housing and defining the annular space between the cam sleeve and slip housing, the cam surfaces extending radially outward from the cam sleeve; and an upper bearing for supporting the mandrel on the cam sleeve while permitting the mandrel to rotate relative to the cam sleeve and slip housing when the slips engage the casing.
 24. The liner hanger as described in claim 23 wherein the slip housing is profiled so as to enlarge the annular space and thereby increase fluid flow bypass.
 25. The liner hanger as described in claim 23 wherein the spring is a flat spring secured to each slip and extending either side of the opening for connecting between the slip housing and the slip.
 26. The liner hanger as described in claim 23 wherein the actuator is a hydraulic portion comprising: a tubular piston housing formed on the mandrel and defining an cylindrical space therebetween; a piston positioned within the cylindrical space and axially moveable therein, the piston being in fluid communication with a bore of the mandrel for actuating the piston from a non-actuated, downhole position to an uphole actuated position as a result of pressure increases in the bore of the mandrel; and a shear screw connected between the mandrel and the slip housing so as to prevent axial movement of the slip housing during insertion of the liner hanger into the wellbore.
 27. A liner hanger for use in hanging a liner inside an existing casing in a wellbore, the liner hanger comprising: a tubular mandrel having a slip housing mounted thereon, the slip housing being axially moveable relative to the mandrel; one or more sets of circumferentially spaced slips, each slip being housed in a slip opening in the slip housing, each of the one or more sets of slips being spaced axially along the slip housing, a cam sleeve positioned between the mandrel and the slip housing and defining an annular space between the cam sleeve and slip housing, the annular space having an inlet and an outlet for permitting the flow of fluids through the annular space, the cam sleeve having cam surfaces extending radially outward for urging the slips on the slip housing to a radially extended position; an upper bearing for supporting the mandrel on the cam sleeve while permitting the mandrel to rotate relative to the cam sleeve and slip housing when the slips engage the casing; and an actuator acting between the mandrel and the slip housing for axially moving the slip housing and engaging the slips with the cam surfaces for causing the slips to move from a radially stowed position to a radially extended position for engaging the existing casing.
 28. The liner hanger as described in claim 27 further comprising a spring for biasing each slip to a radially stowed position towards the mandrel.
 29. The liner hanger as described in claim 27 wherein the slip housing is profiled so as to enlarge the annular space therebetween and increase fluid flow bypass.
 30. The liner hanger as described in claim 27 wherein the actuator is a hydraulic portion comprising: a tubular piston housing formed on the mandrel and defining an cylindrical space therebetween; and a piston positioned within the cylindrical space and axially moveable therein, the piston being in fluid communication with a bore of the mandrel for actuating the piston from a non-actuated, downhole position to an uphole actuated position as a result of pressure increases in the bore of the mandrel.
 31. The liner hanger as described in claim 27 further comprising a shear screw connected between the mandrel and the slip housing so as to prevent axial movement of the slip housing during insertion of the liner hanger into the wellbore.
 32. The liner hanger as described in claim 27 wherein the upper bearing supporting the cam sleeve is a taper bearing.
 33. The liner hanger as described in claim 27 further comprising a collet system between the mandrel and slip housing for retaining the slip housing in a downhole non-actuated position during insertion of the liner hanger into the wellbore.
 34. The liner hanger as described in claim 33 wherein the collet system comprises: a collet connected to the slip housing and normally engaged in a corresponding profile on the mandrel; a collet housing adapted to the slip housing and forming an annular space between the collet and the collet housing; a collet retainer positioned in the annular space in a downhole position for retaining the collet in the profile in the mandrel and axially moveable therein to an uphole position for releasing the collet from the profile in the mandrel; and a shear screw between the collet retainer and the collet housing for temporarily restraining the collet retainer in the downhole position.
 35. The liner hanger as described in claim 34 wherein the collet retainer further comprises a profiled inner surface for alignment with the collet when the collet retainer is moved axially uphole and accepting the collet when released radially from the profile in the mandrel.
 36. The liner hanger as described in claim 27 further comprising mechanical supports formed on either side of the opening in the slip housing at a downhole end of the slips for further supporting the slips in the extended position.
 37. The liner hanger as described in claim 36 wherein the supports are formed as tabs further comprising slits formed in the housing above and below each tab at an interface between the tab and the slip housing to ensure bending of the tab under stress.
 38. The liner hanger as described in claim 27 wherein the slip housing further comprises a plurality of additional openings therethrough to improve fluid bypass.
 39. The liner hanger as described in claim 27 having two or more sets of circumferentially spaced slips, housed in a plurality of openings in the slip housing, each of the one or more sets of slips being spaced axially along the slip housing. 